Acceleration transducer

ABSTRACT

An acceleration transducer defines a rectangular coordinate system with two orthogonal horizontal axes that are both normal to a vertical axis and includes a main body defining tangential side faces arranged tangentially to the vertical axis, and normal side faces arranged normally to the vertical axis. The transducer includes exactly three piezoelectric elements and three seismic masses. Exactly one piezoelectric element is secured to each of the three tangential side faces, and exactly one seismic mass is secured to each of the three piezoelectric elements. Each piezoelectric element has a high sensitivity for a shear force exerted by the attached seismic mass along a principal tangential axis that is another one of the three axes for each of the three piezoelectric elements.

FIELD OF THE INVENTION

The present invention relates to an acceleration transducer that can beattached to an object and in which movement of a seismic mass against apiezoelectric element lodged against a rigid main body generateselectric charges that are collected and processed to yield measurementsof forces indicative of acceleration of the object.

BACKGROUND OF THE INVENTION

Accelerations of a physical object are measured in numerous widelyvaried applications such as robotics, energy generation, transportation,and so on. For this purpose, accelerations are detected in the form ofshocks that act onto the physical object and of vibrations of thephysical object. Accelerations are indicated as multiples of thegravitational acceleration g=9.81 msec⁻². Typical ranges of detectedaccelerations are +/−500 g in measuring ranges from 2 Hz to 10 kHz. Anacceleration transducer is secured to the physical object for detectingaccelerations.

The document CH399021A1, which corresponds to applicant's U.S. Pat. No.3,673,442 to Sonderegger, which is hereby incorporated herein in itsentirety by this reference for all purposes, provides an accelerationtransducer of the above-mentioned type comprising a seismic mass, apiezoelectric system and a main body. The acceleration transducerincludes a housing that contains the seismic mass, the piezoelectricsystem and the main body and serves to protect them from harmfulenvironmental impacts. The acceleration transducer is attached to thephysical object by means of the housing. When an acceleration occurs,the seismic mass exerts a force that is proportional to its accelerationonto the piezoelectric system. The piezoelectric system comprises aplurality of flat discs made of piezoelectric material having a highsensitivity for the longitudinal piezoelectric effect. Under the actionof the exerted force, the piezoelectric material generates piezoelectriccharges, and a magnitude of the piezoelectric charges generated isproportional to the magnitude of the force. With the longitudinalpiezoelectric effect, piezoelectric charges are generated on those facesof the discs on which the force acts as the normal force. Each disc hastwo faces on which piezoelectric charges with opposite polarity aregenerated. Furthermore, the piezoelectric system comprises thinelectrodes made of electrically conductive material for electricallyconducting the piezoelectric charges from the two end faces. Eachelectrode has a surface having the size of an end face. With itssurface, the electrode is in direct and full contact with the end face.In addition, the piezoelectric system is mechanically pre-loaded betweenthe seismic mass and the main body by means of a pre-loading sleeve.This mechanical pre-loading seals microscopic pores between the endfaces and the electrodes so that all generated piezoelectric charges canbe tapped; this sealing by preloading is important for linearity of theacceleration transducer, linearity meaning the ratio of the number ofpiezoelectric charges generated by the force and the magnitude of theforce that generates the piezoelectric charges. The piezoelectriccharges can be transmitted electrically and represent the accelerationsignals. Electrically transmitted acceleration signals may beelectrically transduced in a converter unit.

DE69405962T2, which corresponds to U.S. Pat. No. 6,094,984 to Hiroshi etal, which is hereby incorporated herein in its entirety by thisreference for all purposes, also describes an acceleration transducercomprising a seismic mass and a piezoelectric system on a printedcircuit board. The acceleration transducer detects accelerationsaccording to the transverse shear effect as a shear force that actsalong an axis. The piezoelectric system is arranged between the seismicmass and the printed circuit board. The converter unit is located on theprinted circuit board.

Thus, the piezoelectric system of CH399021A1 is only sensitive to anormal force along one axis. Furthermore, the piezoelectric system ofDE69405962T2 is only sensitive to a shear force along one axis. However,it would be desirable to have acceleration transducers that are able tosimultaneously detect accelerations along a plurality of axes of arectangular coordinate system.

The document RU1792537C1 discloses an acceleration transducer capable ofdetecting accelerations in three physical dimensions. To a cube-shapedmain body with six surfaces are attached a piezoelectric system with sixflat discs made of piezoelectric material and six seismic masses. Twosurfaces each are oriented in a direction normal to one of three axesthat are perpendicular to each other; this axis will be referred to asthe normal axis hereinafter. At each of the six surfaces, a flat disc isintroduced between the surface and a seismic mass. The discs aremechanically pre-loaded against the main body by means of an externalpre-loading housing. Thus, the piezoelectric system comprises a pair ofdiscs for each of three normal axes. The discs have a high sensitivityfor the transverse shear effect. With the transverse shear effect,piezoelectric charges are generated on those end faces of the discs onwhich a shear force acts tangentially to the normal axis; this axis isreferred to as the principal tangential axis hereinafter. Further, thepiezoelectric system comprises electrodes made of electricallyconductive material for picking off (receiving) the piezoelectriccharges from the end faces of the discs.

According to RU1792537C1, the piezoelectric system comprises a pair ofdiscs made of piezoelectric material and exhibiting a high sensitivityfor a shear force acting along a principal tangential axis for each ofthree normal axes.

Unfortunately, it cannot be avoided that piezoelectric material has moreor less high sensitivities for shear forces acting along different axes.Thus, piezoelectric material that has a high sensitivity for a shearforce along the principal tangential axis also exhibits a sensitivity,albeit low, for a shear force acting along an axis perpendicular to theprincipal tangential axis and perpendicular to the normal axis; thisaxis will be referred to as the secondary tangential axis in thefollowing. Each of these shear forces, i.e., the one acting along theprincipal tangential axis as well as the one acting along the secondarytangential axis, generates piezoelectric charges on the end faces of thediscs. As an example, quartz being a piezoelectric material has a highsensitivity for a shear force along the principal tangential axis thatis higher by a factor of 7 than its low sensitivity for a shear forcethat acts along the secondary tangential axis.

Therefore, the low sensitivity of the piezoelectric material for a shearforce that acts along the secondary tangential axis may falsify thedetection of the shear force along the principal tangential axis, andthe respective piezoelectric charges will be referred to aspiezoelectric interference charges hereinafter. To avoid thisfalsification, RU1792537C1 tries to deal with piezoelectric interferencecharges by electrically connecting the pair of discs with oppositepolarity in series for each of the three normal axes. This solution hasthe advantage that a shear force acting along the secondary tangentialaxis will generate the same number of piezoelectric interference chargeson the end faces of each of the two discs, which piezoelectricinterference charges, however, have the opposite polarity and neutralizeeach other when tapped in series.

Moreover, the document EP0546480A1, which corresponds to applicant'sU.S. Pat. No. 5,512,794 to Kuebler et al, which is hereby incorporatedherein in its entirety by this reference for all purposes, describes anacceleration transducer that comprises a piezoelectric system fordetecting accelerations with high sensitivity according to thetransverse shear effect as shear forces acting along three principaltangential axes that are perpendicular to each other. In an embodimentas shown in FIG. 8 , the piezoelectric system consists of six discs madeof piezoelectric material, and a pair of discs with opposite polarity iselectrically connected in series for each of the three principaltangential axes. The acceleration transducer needs only three seismicmasses, one for each of the three principal tangential axes.Piezoelectric interference charges originating from shear forces alongthe secondary tangential axes are neutralized for each of the threeprincipal tangential axes when they are tapped in series.

Furthermore, U.S. Pat. No. 5,539,270 to Kaji et, which is herebyincorporated herein in its entirety by this reference for all purposes,relates to an acceleration transducer for detecting accelerations inthree physical dimensions. A piezoelectric system for each dimension isprovided, and each piezoelectric system comprises two plates made ofpiezoelectric material. End faces facing each other of the two platesare materially bonded to each other. The material connection iselectrically insulating. On those end faces of the plates that face awayfrom each other are attached electrodes that pick off piezoelectriccharges generated under the action of a normal force. The threepiezoelectric systems are mechanically attached to a support. Thesupport comprises electrical conductors for conducting the piezoelectriccharges away from the electrodes. However, seismic masses are notprovided.

There is often limited space available for attaching the accelerationtransducer to the physical object. Therefore, the accelerationtransducer should have small outer dimensions of less than 50 cm³.Furthermore, measuring frequencies of more than 10 kHz are desired.Also, the acceleration transducer should have a small weight since itsresonant frequency is inversely proportional to its weight.

U.S. Pat. No. 7,066,026 to Deng, which is hereby incorporated herein inits entirety by this reference for all purposes, relates to an acousticvector sensor or particle sensor that employs three piezoelectriccrystals in the form of relaxor single crystals, which are crystalplates cut at a special orientation such that they provide zero orminimum responses in the transverse directions, but have maximumpiezoelectric response in the sensing direction. The relaxor crystalsare mounted between a rigid case and a proof mass with a reduced bondingarea between the proof mass and the relaxor crystal to try to deal withthe clamping effect associated with the relaxor crystal.

The document CN201152880Y discloses an acceleration transducercomprising a piezoelectric system, a seismic mass, and a main body. Themain body has a cylindrical shape and terminates in a normal end facealong a vertical axis. Along a normal axis perpendicular to the verticalaxis the piezoelectric system is mechanically pre-loaded between themain body and the seismic mass by means of a pre-loading sleeve. Thepre-loading sleeve is hollow-cylindrical in shape and ends in a lateralsurface in a plane of the normal end face of the main body. The seismicmass is formed as a disc and also ends in a lateral surface in the planeof the normal end face of the main body. A converter unit in the form ofa charge amplifier is arranged in this plane on the lateral surfaces ofthe pre-loading sleeve and seismic mass, as well as on the normal endface of the main body, thus saving space.

However, this arrangement of the converter unit on lateral surfaces ofthe pre-loading sleeve and seismic mass as well as on the normal endface of the main body presents a disadvantage of the introduction of aforce shunt that forms between the seismic mass and the main body. As aresult, the seismic mass no longer can oscillate freely under the effectof an acceleration, and a force acting onto the piezoelectric system dueto the inertia of the seismic mass is impeded so that the force is nolonger proportional to the acceleration. In addition, the piezoelectriccharges generated by the piezoelectric material are no longerproportional to the acceleration to be detected. Thus, the force shuntfalsifies the acceleration measurement.

EXEMPLARY OBJECTS AND SUMMARY OF THE INVENTION

One object of the present invention to provide an accelerationtransducer capable of simultaneously detecting an acceleration in aplurality of physical dimensions. Another object of the invention is toprovide an acceleration transducer that detects an acceleration as freefrom falsification as possible. According to a further object of thepresent invention, the acceleration transducer shall have small outerdimensions and a low weight. An additional object of the invention is toprovide an acceleration transducer configured for high measuringfrequencies of over 10 kHz. And according to a still further object ofthe invention, the configuration of the acceleration transducer shouldlend itself to being produce at low cost.

At least one of these objects has been achieved by the featuresdescribed herein.

The invention relates to an acceleration transducer comprising at leastone piezoelectric element, at least one seismic mass and a main body.The acceleration transducer is disposed in a rectangular coordinatesystem with three axes, and one of said three axes is a vertical axis.The main body comprises tangential side faces arranged tangentially tothe vertical axis. The main body further comprises normal side facesarranged normally to the vertical axis. The acceleration transducercomprises exactly three piezoelectric elements and three seismic masses.To each of three tangential side faces of the main body is attachedexactly one of the three piezoelectric elements. Likewise, to each ofthe three piezoelectric elements is attached exactly one of the threeseismic masses. Upon acceleration of a seismic mass, a shear forceproportional to said acceleration is exerted by the seismic mass ontothe piezoelectric element. Moreover, each of the three piezoelectricelements has a high sensitivity for a shear force along a principaltangential axis that is exerted by the seismic mass attached thereto.Additionally, the principal tangential axis is a different one of thethree axes for each of the three piezoelectric elements.

Thus, the acceleration transducer according to the invention is able tosimultaneously detect an acceleration along three axes. For thispurpose, each of the three axes is provided with exactly onepiezoelectric element having a high sensitivity for the shear force tobe detected and detecting the shear force to be detected independentlyof the other two piezoelectric elements. The acceleration transduceraccording to the invention has a markedly compact design since itrequires only three piezoelectric elements and three seismic masses, andthe three piezoelectric elements and three seismic masses are arrangedin a space-saving manner on three tangential side faces of the mainbody. In contrast, RU1792537C1 teaches the use of six piezoelectricelements and six seismic masses secured to six surfaces of a cube-shapedmain body. Thus, only half as many piezoelectric elements and seismicmasses are required according to the present invention, thereby reducingthe overall space needed accordingly.

The disclosure herein suffices to inform persons of ordinary skill inthe field of the invention of further advantageous embodiments of theinvention not explicitly described herein.

BRIEF DESCRIPTION OF THE DRAWINGS OF EXEMPLARY EMBODIMENTS

In the following, the invention will be explained in more detail bymeans of exemplary embodiments referring to the figures in which:

FIG. 1 shows a view of a portion of a first embodiment of anacceleration transducer comprising a transducer unit;

FIG. 2 shows a view of a portion of a second embodiment of anacceleration transducer comprising a transducer unit;

FIG. 3 shows a view of a transducer unit comprising a converter unit ofthe acceleration transducer according to FIG. 1 ;

FIG. 4 shows a view of a transducer unit comprising a converter unit ofthe acceleration transducer according to FIG.2;

FIG. 5 shows an exploded view of a portion of the transducer unitaccording to FIGS. 1 to 4 ;

FIG. 6 shows a top view of the transducer unit according to FIGS. 1 to 5under the effect of an acceleration;

FIG. 7 shows a first view of a first embodiment of a piezoelectricelement of the transducer unit according to FIGS. 1 to 5 ;

FIG. 8 shows a second view of the embodiment of the piezoelectricelement according to FIG. 7 ;

FIG. 9 shows a first view of a second embodiment of a piezoelectricelement of the transducer unit according to FIGS. 1 to 5 ;

FIG. 10 shows a second view of the second embodiment of thepiezoelectric element according to FIG. 9 ;

FIG. 11 shows a schematic representation of the transmission of thepiezoelectric charges of the transducer unit according to FIGS. 1 to 5 ;

FIG. 12 shows a schematic representation of a high-pass filter of theconverter unit of the transducer unit according to FIG. 11 ;

FIG. 13 shows a schematic representation of a low-pass filter of theconverter unit of the transducer unit according to FIG. 11 ;

FIG. 14 shows a view of a first step in the assembly of the accelerationtransducer according to FIG. 2 in which signal conductors are introducedinto a housing;

FIG. 15 shows a view of a second step in the assembly of theacceleration transducer according to FIG. 2 in which the signalconductors are cast in casting compound within the housing;

FIG. 16 shows a view of a third step in the assembly of the accelerationtransducer according to FIG. 2 in which the signal conductors cast incasting compound are exposed in some areas within the housing;

FIG. 17 shows a view of a fourth step in the assembly of theacceleration transducer according to FIG. 2 in which the transducer unitis introduced into the housing; and

FIG. 18 shows a view of a fifth step in the assembly of the accelerationtransducer according to FIG. 2 in which the converter unit of thetransducer unit is electrically connected.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION

FIGS. 1 and 2 show a portion of each of two embodiments of anacceleration transducer 1 according to the invention. The accelerationtransducer 1 is arranged in a rectangular coordinate system with threeaxes x, y, z also referred to as the transverse axis x, the longitudinalaxis y and the vertical axis z. Acceleration transducer 1 comprises atransducer unit 1.1, a housing 1.2, a converter unit 1.3 and a signaloutput 1.4.

The housing 1.2 protects the acceleration transducer 1 from harmfulenvironmental impacts such as contamination (dust, moisture, etc.) andfrom electrical and electromagnetic interference effects in the form ofelectromagnetic radiation. The housing 1.2 is made of mechanicallyresistant material such as pure metals, nickel alloys, cobalt alloys,iron alloys, etc. The housing 1.2 has a rectangular cross-section with awidth along the transverse axis x of preferably less than 5 cm, with alength along the longitudinal axis y of preferably less than 5 cm, andwith a height along the vertical axis z of preferably less than 2 cm sothat it has small outer dimensions defining a volume of less than 50cm³. As schematically shown in FIGS. 14-16 for example, the interior ofthe housing 1.2 has the shape of a pot or a well and is defined by ahousing opening 1.20 and a housing bottom 1.23. The dimension of thehousing opening 1.20 is such that the transducer unit 1.1 can beintroduced into the housing 1.2 and be secured to the housing bottom1.23 and connected to the signal output 1.4 through the housing opening1.20. In the context of the present invention, the term “connection” isunderstood to mean an electrical and mechanical connection. The housingopening 1.20 can be sealed by a housing cover 1.21. Preferably, it issealed by means of material bonding such as welding, soldering, gluing,etc. In use, the acceleration transducer 1 is configured to be attachedto a physical object whose acceleration is to be detected by means ofthe housing 1.2. Any method of attachment may be chosen.

As schematically shown in FIG. 3 for example, the transducer unit 1.1comprises first, second and third piezoelectric elements 10, 10′, 10″,first, second and third seismic masses 11, 11′, 11″ and a main body 12.The first, second and third piezoelectric elements 10, 10′, 10″ and thefirst, second and third seismic masses 11, 11′, 11″ are attached to themain body 12. The main body 12, in turn, is attached to the housing 1.2.Preferably, though not shown in FIG. 3 , the main body 12 is attached tothe bottom 1.23 of the housing 1.2 by means of material bonding such asgluing, soldering, etc.

The first, second and third piezoelectric elements 10, 10′, 10″ are madeof piezoelectric material such as quartz (SiO₂ single crystal), calciumgallo-germanate (Ca₃Ga₂Ge₄O₁₄ or CGG), langasite (La₃Ga₅SiO₁₄ or LGS),tourmaline, gallium orthophosphate, piezoceramics, etc. The first,second, and third piezoelectric elements 10, 10′, 10″ have a highsensitivity for the force to be measured. The first, second and thirdpiezoelectric elements 10, 10′, 10″ are rectangular in cross-section,with a surface area of preferably less than 1 cm² and a thickness ofpreferably less than 2 mm. This disclosure suffices to inform thoseskilled in the art that the present invention may be carried out usingpiezoelectric elements with different shapes and cross-sections such ascircular, etc.

Preferably, the first, second and third seismic masses 11, 11′, 11″ aremade of high-density material such as iridium, platinum, tungsten, gold,etc. For small outer dimensions of the acceleration transducer 1, thefirst, second and third seismic masses 11, 11′, 11″ will have a highdensity of preferably more than 19 g/cm³. The first, second and thirdseismic masses 11, 11′, 11″ are rectangular in cross-section having asurface area that is preferably smaller than 1 cm² and a thickness thatis preferably smaller than 5 mm. Those skilled in the art being aware ofthe present invention may also use seismic masses with different shapesand cross-sections such as circular, etc. Furthermore, a person skilledin the art may use seismic masses that are made of material with lowerdensity such as steel, ceramics, etc.

The main body 12 is made of mechanically stiff material having a lowdensity such as Al₂O₃, ceramics, Al₂O₃ ceramics, sapphire, etc.Mechanical stiffness of the main body 12 is required for inelastictransmission of an acceleration to be detected from the housing 1.1 ontothe first, second and third seismic masses 11, 11′, 11″. For highmechanical stiffness of the acceleration transducer 1, the main body 12has a high modulus of elasticity of preferably 350 GPa to 470 GPa. For alow weight of the acceleration transducer 1, the main body 12 has a lowdensity of preferably less than 4 g/cm³. As schematically shown in FIG.5 for example, the main body 12 is preferably a cube with six side faces12.1, 12.2, 12.3, 12.4, 12.6, 12.7. Four tangential side faces 12.1,12.2, 12.3, 12.4 are arranged tangentially with respect to the verticalaxis z and parallel to the vertical axis z, which is disposed normallyto the two normal side faces 12.6, 12.7. The size of each of the sidefaces 12.1, 12.2, 12.3, 12.4, 12.6, 12.7 desirably is the same size.Each side face 12.1, 12.2, 12.3, 12.4, 12.6, 12.7 desirably has asurface area of less than 1 cm². In the context of the presentinvention, the adverb “essentially” has the meaning of “+/−10%”. Each ofthe x, y, z axes is normal to two of the side faces, and each of the xand y axes is parallel to two of the side faces. Those skilled in theart and knowing the present invention may use a main body with adifferent shape and differently shaped surfaces such as circular, etc.

As schematically shown in FIGS. 3 and 4 , a first seismic mass 11 and afirst piezoelectric element 10 are attached to a first tangential sideface 12.1 of the main body 12. A second seismic mass 11′ and a secondpiezoelectric element 10′ are attached to a second tangential side face12.2 of the main body 12. A third seismic mass 11″ and a thirdpiezoelectric element 10″ are attached to a third tangential side face12.3 of the main body 12. Here, each of the piezoelectric elements 10,10′, 10″ is arranged between a tangential side face 12.1, 12.2, 12.3 anda seismic mass 11, 11′, 11″, respectively. As schematically shown inFIGS. 5 and 6 , a fourth tangential side face 12.4 is vacant.

The attachment of the first, second and third seismic masses 11, 11′,11″ and the first, second and third piezoelectric elements 10, 10′, 10″on the main body 12 is achieved by first, second and third innerconnection means 15, 15′, 15″ and first, second and third outerconnection means 16, 16′, 16″. Each of these attachments desirably iscarried out by means of material bonding such as gluing, thermalcompression bonding, etc. Such mechanical attachment of the first,second and third seismic masses 11, 11′, 11″ and the first, second andthird piezoelectric elements 10, 10′, 10″ by means of first, second andthird inner connecting means 15, 15′, 15″ and first, second and thirdouter connecting means 16, 16′, 16″ facilitates the assembly of theacceleration transducer 1 and can be performed quickly and in acost-effective manner.

The first, second and third inner connecting means 15, 15′, 15″ and thefirst, second and third outer connecting means 16, 16′, 16″ desirably isan adhesive that can be chemically cured or physically hardened or acombination of adhesives that can be chemically cured and physicallyhardened. Preferably, each of the first, second and third innerconnecting means 15, 15′, 15″ and the first, second and third outer 16,16′, 16″ consists of an adhesive such as epoxy, polyurethane,cyanoacrylate, methyl methacrylate, etc. Each of the first, second andthird inner connecting means 15, 15′, 15″ and the first, second andthird outer connecting means 16, 16′, 16″ is an electrical insulatorhaving an electrical resistivity of more than 10¹²Ωmm²/m.

As shown in FIG. 5 , the first piezoelectric element 10 is attached viaa first inner connecting means 15 to the first tangential side face12.1. The first seismic mass 11 is attached via a first outer connectingmeans 16 to the first piezoelectric element 10. The second piezoelectricelement 10′ is attached via a second inner connecting means 15′ to thesecond tangential side face 12.2. The second seismic mass 11′ isattached via a second external connection means 16′ to the secondpiezoelectric element 10′. The third piezoelectric element 10″ isattached via a third inner connecting means 15″ to the third tangentialside face 12.3. The third seismic mass 11″ is attached via a third outerconnecting means 16″ to the third piezoelectric element 10″.

Preferably, each of the first, second and third piezoelectric elements10, 10′, 10″ is attached respectively by the first, second and thirdinner connecting means 15, 15′, 15″ and the first, second and thirdouter connecting means 16, 16′, 16″ to the first, second and thirdseismic masses 11, 11′, 11″ and the main body 12 in a manner resistantto shear forces.

Each first, second and third inner connecting means 15, 15′, 15″ andeach first, second and third outer connecting means 16, 16′, 16″ isrectangular in cross-section having a surface area of preferably lessthan 1 cm² and a thickness of preferably less than 0.1 mm. Those skilledin the art being aware of the present invention may also use inner andouter connecting means of different shapes and cross-sections such ascircular, etc.

As schematically shown in FIG. 7 , the first, second and thirdpiezoelectric elements 10, 10′, 10″ have a high sensitivity for thetransverse shear effect along a principal tangential axis h and have alow sensitivity for the transverse shear effect along a secondarytangential axis n as well as a low sensitivity for the piezoelectrictransverse effect along a normal axis a. The principal tangential axis his a different one of the three axes x, y, z for each of the threepiezoelectric elements 10, 10′, 10″. The secondary tangential axis n isa different one of the three axes x, y, z for each of the threepiezoelectric elements 10, 10′, 10″. The normal axis a is a differentone of the three axes x, y, z for each of the three piezoelectricelements 10, 10′, 10″.

The transverse shear effect along the principal tangential axis h or thesecondary tangential axis n generates piezoelectric charges on the sameend faces of the first, second and third piezoelectric elements 10, 10′,10″ as those onto which a shear force is applied along the principaltangential axis h or the secondary tangential axis n.

The piezoelectric transverse effect generates piezoelectric charges onlateral surfaces of the first, second, and third piezoelectric elements10, 10′, 10″, which lateral surfaces are perpendicular to the end facesof the first, second, and third piezoelectric elements 10, 10′, 10″ ontowhich a normal force acts along a normal axis a.

The higher the sensitivity, the more piezoelectric charges are generatedfor a given amount of force. For the purposes of the present invention,the terms “high sensitivity” and “low sensitivity” are related to eachother. Each of the three piezoelectric elements 10, 10′, 10″ with a highsensitivity for a shear force along a principal tangential axis hgenerates at least by a factor of 5, more piezoelectric charges per unitforce compared to a low sensitivity for a shear force along a secondarytangential axis n or for a normal force along a normal axis a.

Thus, the piezoelectric material is chosen so that mainly piezoelectriccharges generated by the transverse shear effect along the principaltangential axis h are taken into account in the detection of anacceleration. In the disclosure herein, the piezoelectric chargesgenerated according to the transverse shear effect along the secondarytangential axis n and those generated according to the piezoelectrictransverse effect along the normal axis a will be referred to aspiezoelectric interference charges.

FIG. 6 schematically shows a top view of the transducer unit 1.1 duringan acceleration. The acceleration causes the first, second and thirdseismic masses 11, 11′, 11″ to exert a force F onto end faces of thefirst, second and third piezoelectric elements 10, 10′, 10″. In theexample schematically shown in FIG. 6 , the force F acts parallel alongthe longitudinal axis y as shown by the direction in which the arrowsdesignated F are pointing.

Referring to FIG. 6 , the first piezoelectric element 10 has a highsensitivity for a shear force along the longitudinal axis y being itsprincipal tangential axis h. Since the force F acts along thelongitudinal axis y, the first piezoelectric element 10 generatespiezoelectric charges for the force F according to the transverse sheareffect on its end faces. The first piezoelectric element 10 has a lowsensitivity for a shear force acting along the vertical axis z being itssecondary tangential axis n, and a low sensitivity for a normal forceacting along the transverse axis x being its normal axis a. The force Facts along the longitudinal axis y where it exerts a torque around thevertical axis z. The first piezoelectric element 10 generatespiezoelectric interference charges according to the transverse sheareffect on its end faces for this torque.

Referring to FIG. 6 , the second piezoelectric element 10′ exhibits ahigh sensitivity for a shear force along the transverse axis x being itsprincipal tangential axis h. However, the force F acts along thelongitudinal axis y, and the second piezoelectric element 10′ does notgenerate piezoelectric charges on its end faces for the force F actingin the direction along the longitudinal axis y. The second piezoelectricelement 10′ has a low sensitivity for a shear force acting along thevertical axis z being its secondary tangential axis n, and a lowsensitivity for a normal force acting along the longitudinal axis ybeing its normal axis a. Since the force F acts along the longitudinalaxis y, the second piezoelectric element 10′ generates piezoelectricinterference charges according to the piezoelectric transverse effect onthe lateral surfaces of the second piezoelectric element 10′.

Moreover, still referring to FIG. 6 , the third piezoelectric element10″ exhibits a high sensitivity for a shear force along the verticalaxis z being its principal tangential axis h. However, the force F actsas a shear force along the longitudinal axis y, and the thirdpiezoelectric element 10″ does not generate piezoelectric charges on itsend faces for the force F acting as a shear force along the longitudinalaxis y. The third piezoelectric element 10″ has a low sensitivity for ashear force acting along the longitudinal axis y being its secondarytangential axis n, and a low sensitivity for a normal force along thetransverse axis x being its normal axis a. The force F acts along thelongitudinal axis y and exerts a torque around the vertical axis z. Thethird piezoelectric element 10″ generates piezoelectric interferencecharges according to the transverse shear effect on its end faces forthis torque.

FIGS. 7 and 8 show a detailed view of a first embodiment of a first,second or third piezoelectric element 10, 10′, 10″ of the transducerunit 1.1. FIGS. 9 and 10 show a detailed view of a second embodiment ofa first, second or third piezoelectric element 10, 10′, 10″ of thetransducer unit 1.1. The first, second or third piezoelectric element10, 10′, 10″ comprises two end faces 110, 120 and four lateral surfaces130, 140, 150, 160.

Each of the three piezoelectric elements 10, 10′, 10″ comprises a firstend face 110 and a second end face 120. Wherein each end face 110, 120lies in a plane defined by the principal tangential axis h and thesecondary tangential axis n. In each plane defining an end face 110,120, the secondary tangential axis n is perpendicular to the principaltangential axis h. Further, the normal axis a is normal to the planedefining an end face 110, 120. Under the action of a shear force alongthe principal tangential axis h, each of the three piezoelectricelements 10, 10′, 10″ generates piezoelectric charges on the two endfaces 110, 120. Moreover, under the action of a shear force along thesecondary tangential axis n, each of the three piezoelectric elements10, 10′, 10″ generates piezoelectric interference charges on the two endfaces 110, 120. Each of the three piezoelectric elements 10, 10′, 10″comprises lateral surfaces 130, 140, 150, 160. The lateral surfaces 130,140, 150, 160 are parallel to the normal axis a. The lateral surfaces130, 140, 150, 160 comprise a first lateral surface 130, a secondlateral surface 140, a third lateral surface 150 and a fourth lateralsurface 160. The first lateral surface 130 and the fourth lateralsurface 160 are normal to the secondary tangential axis n of thepiezoelectric element 10, 10′, 10″. The second lateral surface 140 andthe third lateral surface 150 are normal to the principal tangentialaxis h of the piezoelectric element 10, 10′, 10″.

When a normal force acts along the normal axis a, each of the threepiezoelectric elements 10, 10′, 10″ generates piezoelectric interferencecharges on the four lateral surfaces 130, 140, 150, 160.

Thus, the piezoelectric charges generated for the shear force that shallbe measured are generated on only two end faces 110, 120 of thepiezoelectric elements. In addition, piezoelectric interference chargesare generated both on the two end faces 110, 120 and the four lateralsurfaces 130, 140, 150, 160.

An electrically conductive end face coating 111, 121 covers at least insome areas of the end faces 110, 120. A size of the area of theelectrically conductive end face coating 111, 121 may be between 90% and100% of the end faces 110, 120. Similarly, an electrically conductivelateral surface coating 131, 141, 151, 161 covers some areas of thelateral surfaces 130, 140, 150, 160. A size of the area of theelectrically conductive lateral surface coating 131, 141, 151, 161 maybe between 0% and 100% of the lateral surfaces 130, 140, 150, 160. Theelectrically conductive end face coating 111, 121 and the electricallyconductive lateral surface coating 131, 141, 151, 161 may be produced bythermal lamination of a metal film or by metal deposition. Electricallyconductive materials such as copper, copper alloys, gold, gold alloys,aluminum, aluminum alloys, silver, silver alloys, etc., may be used asthe metal. Each of the electrically conductive end face coatings 111,121 and each of the electrically conductive lateral surface coatings131, 141, 151, 161 preferably has a thickness of less than 0.1 mm.

Thus, in accordance with an aspect of the present invention, instead oftrue electrodes, the acceleration transducer 1 only comprises anelectrically conductive end face coating 111, 121 and an electricallyconductive lateral surface coating 131, 141, 151, 161. Thus, inaccordance with an aspect of the present invention, the accelerationtransducer 1 contains fewer components which saves space and reducescosts of production by facilitating the assembly of the accelerationtransducer 1.

Moreover, mechanical pre-loading of the first, second or thirdpiezoelectric element 10, 10′, 10″ is not required due to theelectrically conductive end face coating 111, 121 and the electricallyconductive lateral surface coating 131, 141, 151, 161. The reason isthat the electrically conductive end face coating 111, 121 and theelectrically conductive lateral surface coating 131, 141, 151, 161 arein material contact with the end faces 110, 120 and the lateral surfaces130, 140, 150, 160 and seal microscopic pores in the end faces 110, 120and the lateral surfaces 130, 140, 150, 160. Due to this sealing ofmicroscopic pores, it is no longer necessary to provide the accelerationtransducer 1 with separate pre-loading means such as a pre-loadingsleeve according to CH399021A1 or a pre-loading housing according toRU1792537C1. This results in fewer components which saves space andweight and reduces costs of production by facilitating the assembly ofthe acceleration transducer 1.

Referring to FIGS. 7 and 8 , according to the first embodiment of afirst, second or third piezoelectric element 10, 10′, 10″ the first endface 110 schematically shown in FIG. 7 comprises two first electricallyconductive end face coatings 111, 111′ in some areas thereof and twofirst uncoated end face areas 112, 112′ in some areas thereof.Furthermore, the second end face 120 schematically shown in FIG. 8comprises two more electrically conductive end face coatings 121, 121′,121″ in some areas thereof. The first lateral surface 130 comprises afirst electrically conductive lateral surface coating 131 in some areasthereof, another first electrically conductive lateral surface coating133 in some areas thereof, and a plurality of uncoated first lateralsurface areas 132, 132′, 132″, 132′″, 132″″ in some areas thereof. Thesecond lateral surface 140 schematically shown in FIG. 8 comprises asecond electrically conductive lateral surface coating 141 in some areasthereof and a second uncoated lateral surface area 142 in some areasthereof. The third lateral surface 150 schematically shown in FIG. 7comprises a third electrically conductive lateral surface coating 151 insome areas thereof as well as two third uncoated lateral surface areas152, 152′ in some areas thereof. The fourth lateral surface 160comprises a fourth electrically conductive lateral surface coating 161in some areas thereof.

According to the first embodiment of a first, second, or thirdpiezoelectric element 10, 10′, 10″ as shown in FIGS. 7 and 8 , the twofirst electrically conductive end face coatings 111, 111′, the furtherfirst electrically conductive lateral surface coating 133, and the thirdelectrically conductive lateral surface coating 151 form a firstcontinuous electrically conductive coating 101. The plurality of secondelectrically conductive end face coatings 121, 121′, 121″, the firstelectrically conductive lateral surface coating 131, the secondelectrically conductive lateral surface coating 141, and the fourthelectrically conductive lateral surface coating 161 form a secondcontinuous electrically conductive coating 102.

For the purposes of the present invention, the adjective “continuous”has the meaning of “connected in an electrically conductive manner.” Thefirst continuous electrically conductive coating 101 receives firstpiezoelectric charges that are generated on surfaces of the first,second or third piezoelectric element 10, 10′, 10″ below the firstcontinuous electrically conductive coating 101 as the first accelerationsignals S1. The second continuous electrically conductive coating 102receives second piezoelectric charges that are generated on surfaces ofthe first, second, or third piezoelectric element 10, 10′, 10″ below thesecond continuous electrically conductive coating 102 as the secondacceleration signals S2. The first and second piezoelectric charges haveopposite electrical polarity (or sign). Thus, either the firstpiezoelectric charges have a negative sign and the second piezoelectriccharges have a positive sign, or the first piezoelectric charges have apositive sign and the second piezoelectric charges have a negative sign.

Preferably, the first electrically conductive end face coating 111 andthe first electrically conductive lateral surface coating 131 form thefirst continuous electrically conductive coating 101. Preferably, thesecond electrically conductive end face coating 121 and the furtherfirst electrically conductive lateral surface coating 133 form thesecond continuous electrically conductive coating 102. Preferably, atleast one second, third or fourth electrically conductive lateralsurface coating 141, 151, 161 is part of the first continuouselectrically conductive coating 101 or part of the second continuouselectrically conductive coating 102.

According to the first embodiment of a first, second or thirdpiezoelectric element 10, 10′, 10″ as shown in FIGS. 7 and 8 , the firstand second continuous electrically conductive coatings 101, 102 areelectrically insulated from one another by two first uncoated end faceareas 112, 112′, a plurality of first uncoated lateral surface areas132, 132′, 132″, 132′″, a second uncoated lateral surface area 142 andtwo third uncoated lateral surface areas 152, 152′.

According to the second embodiment of a first, second, or thirdpiezoelectric element 10, 10′, 10″ as shown in FIGS. 9 and 10 , thefirst end face 110 comprises a first electrically conductive end facecoating 111 in some areas thereof and a plurality of first uncoated endface areas 112, 112′, 112″ in some areas thereof. Furthermore, thesecond end face 120 schematically shown in FIG. 10 comprises a pluralityof second electrically conductive end face coatings 121, 121″, 121″ insome areas thereof and a second uncoated end face area 122 in some areasthereof. The first lateral surface 130 comprises a first electricallyconductive lateral surface coating 131 in some areas thereof, twoadditional first electrically conductive lateral surface coatings 133,133′ in some areas thereof, and a plurality of uncoated first lateralsurface areas 132, 132′, 132″ in some areas thereof. The second lateralsurface 140 comprises a second electrically conductive lateral surfacecoating 141 in some areas thereof and a plurality of second uncoatedlateral surface areas 142, 142′, 142″ in some areas thereof. The thirdlateral surface 150 comprises a third electrically conductive lateralsurface coating 151 in some areas thereof and a third uncoated lateralsurface area 152, 152′ in some areas thereof. The fourth lateral surface160 comprises a fourth electrically conductive lateral surface coating161 in some areas thereof.

According to the second embodiment of a first, second or thirdpiezoelectric element 10, 10′, 10″ as shown in FIGS. 9 and 10 , theplurality of first electrically conductive end face coatings 112, 112′,112″ and the two first electrically conductive lateral surface coatings131, 131′ form a first continuous electrically conductive coating 101.The plurality of second electrically conductive end face coatings 121,121′, 121″, the two additional first electrically conductive lateralsurface coatings 133, 133′, the second electrically conductive lateralsurface coating 141, the third electrically conductive lateral surfacecoating 151, and the fourth electrically conductive lateral surfacecoating 161 form a second continuous electrically conductive coating102.

According to the second embodiment of a first, second or thirdpiezoelectric element 10, 10′, 10″ as shown in FIGS. 9 and 10 , theelectrically conductive lateral surface coatings 131, 131′ of the firstcontinuous electrically conductive coating 101 receive piezoelectricinterference charges for the normal force along the normal axis a, whichpiezoelectric interference charges have a polarity opposite to that ofthe piezoelectric interference charges received by the firstelectrically conductive end face coating 111 of the first continuouselectrically conductive coating 101 for the shear force along thesecondary tangential axis n. In addition, the electrically conductivelateral surface coatings 133, 141, 151, 161 of the second continuouselectrically conductive coating 102 receive piezoelectric interferencecharges for the normal force acting along the normal axis a, whichpiezoelectric interference charges have an electrical polarity that isopposite to that of the piezoelectric interference charges received bythe second electrically conductive end face coating 121, 121″, 121′″ ofthe second continuous electrically conductive coating 102 for the shearforce acting along the secondary tangential axis n.

According to the second embodiment of a first, second or thirdpiezoelectric element 10, 10′, 10″ as shown in FIGS. 9 and 10 , thefirst electrically conductive coating 101 and the second electricallyconductive coating 102 are electrically insulated from one another by aplurality of first uncoated end face areas 112, 112′, 112″, a seconduncoated end face area 122, a plurality of first uncoated lateralsurface areas 132, 132′, 132″, a plurality of second uncoated lateralsurface areas 142, 142′, 142″, and a third uncoated lateral surface area152.

A ratio of the size of the first electrically conductive coating 131 andthe size of the further first electrically conductive coating 133 may beadjusted by a relative position and/or size of the first uncoatedlateral surface areas 132, 132′, 132″, 132′″, 132″″ of the first lateralsurface 130. In the context of the invention, the pair of conjunctions“and/or” means that either only one of the conjunctions or both of theconjunctions apply.

A ratio of the size of the first electrically conductive coating 131 andthe size of the further first electrically conductive coating 133 may beadjusted by a relative position of the first uncoated lateral surfaceareas 132, 132′, 132″, 132′″, 132″″ of the first lateral surface 130with respect to the second and third lateral surfaces 140, 150.Depending on the relative position of the first uncoated lateral surfaceareas 132, 132′, 132″, 132′″, 132″″ of the first lateral surface 130that is moved further towards the second lateral surface 140 or furthertowards the third lateral surface 150, the ratio of the size of thefirst electrically conductive coating 131 and the size of the furtherfirst electrically conductive coating 133 may be reduced or increasedaccordingly. According to the first embodiment of a first, second orthird piezoelectric element 10, 10′, 10″ as shown in FIGS. 7 and 8 , thefirst uncoated lateral surface areas 132, 132′, 132′″, 132″″ arepositioned relatively close to the second lateral surface 140. Accordingto the second embodiment of a first, second or third piezoelectricelement 10, 10′, 10″ as shown in FIGS. 9 and 10 , the first uncoatedlateral surface areas 132, 132′, 132″ are positioned at essentially thesame distance from the second 140 and third lateral surface 150.

However, a ratio of the size of the first electrically conductivecoating 131 and the size of the further first electrically conductivecoating 133 may also be adjusted by increasing or decreasing the size ofthe first uncoated lateral surface areas 132, 132′, 132′″, 132″″ of thefirst lateral surface 130. According to the first embodiment of a first,second or third piezoelectric element 10, 10′, 10″ as shown in FIGS. 7and 8 , the first uncoated lateral surface areas 132, 132′, 132″, 132′″,132″″ have essentially twice the size of the further first electricallyconductive coating 133, and the first uncoated lateral surface areas132, 132′, 132′″, 132′″, 132″″ are essentially five times smaller thanthe first electrically conductive coating 131. According to the secondembodiment of a first, second or third piezoelectric element 10, 10′,10″ as shown in FIGS. 9 and 10 , the first uncoated lateral surfaceareas 132, 132′, 132″ have essentially the same size as the firstelectrically conductive coating 131, 131′ and the further firstelectrically conductive coating 133.

Preferably, the electrically conductive lateral surface coatings of thefirst electrically conductive coating 101 receive piezoelectricinterference charges for the normal force along the normal axis a, whichpiezoelectric interference charges have an electrical polarity that isopposite to that of the piezoelectric interference charges received bythe first electrically conductive end face coating of the firstelectrically conductive coating 101 for the shear force acting along thesecondary tangential axis n. In addition, the electrically conductivelateral surface coatings of the second electrically conductive coating102 receive piezoelectric interference charges for the normal forcealong the normal axis a, which piezoelectric interference charges havean electrical polarity opposite to that of the piezoelectricinterference charges received by the second electrically conductive endface coating of the second electrically conductive coating 102 for theshear force along the secondary tangential axis n.

Preferably, a size of the electrically conductive lateral surfacecoatings of the first continuous electrically conductive coating 101 issuch that the number of piezoelectric interference charges received forthe normal force along the normal axis a by the electrically conductivelateral surface coatings is essentially the same as the number ofpiezoelectric interference charges received for the shear force alongthe secondary tangential axis n by the first electrically conductive endface coating of the first continuous electrically conductive coating101. Furthermore, the electrically conductive lateral surface coatingsof the second continuous electrically conductive coating 102 receiveessentially the same number of piezoelectric interference charges forthe normal force along the normal axis a as are received for the shearforce along the secondary tangential axis n by the second electricallyconductive end face coating of the second continuous electricallyconductive coating 102.

In contrast to RU1792537C1, the shear force is detected according to theinvention by only one piezoelectric element 10, 10′, 10″ per axis. Thus,it is not possible to eliminate piezoelectric interference chargesresulting from a shear force acting along a secondary tangential axis nand which would falsify the measurement of the shear force along theprincipal tangential axis h by connecting two piezoelectric elementswith opposite polarity per axis in series. Therefore, the accelerationtransducer 1 of the invention uses a different solution. This is basedon the fact that the piezoelectric material also generates piezoelectricinterference charges for a normal force acting along a normal axis a onlateral surfaces 130, 140, 150, 160. These piezoelectric interferencecharges also falsify the detection of the shear force along theprincipal tangential axis h. For this reason, these piezoelectricinterference charges are usually not picked off from the lateralsurfaces 130, 140, 150, 160. However, it has now been found that theoccurrence of a shear force along a secondary tangential axis n isaccompanied by a normal force acting along a normal axis a. Whilepiezoelectric interference charges are generated on the end faces 110,120 for the former, piezoelectric interference charges are generated onthe lateral surfaces 130, 140, 150, 160 for the latter. These two typesof piezoelectric interference charges interfere with the detection ofthe shear force along the principal tangential axis h. By using suitablefirst and second continuous electrically conductive coatings 101, 102,it is possible to electrically connect the end faces 110, 120 and thelateral surfaces 130, 140, 150, 160 in series and to eliminate thepiezoelectric interference charges that interfere with the detection ofthe shear force along the principal tangential axis h. This advantageousresult is accomplished by having an equal number of piezoelectricinterference charges of opposite electrical polarity, cancel each otherto yield a zero net charge.

FIG. 11 is a schematic representation of the transmission of thepiezoelectric charges of the transducer unit 1.1. A portion of a first,second or third piezoelectric element 10, 10′, 10″ with the firstlateral surface 130 and a portion of the converter unit 1.3 as well as aportion of the signal output 1.4 are shown.

The converter unit 1.3 is capable of converting first accelerationsignals S1. The converter unit 1.3 comprises at least first and secondpiezoelectric element conductors 13.1, 13.1′, 13.1″, 13.2, 13.2′, 13.2″,at least first and second main body conductors 13.3, 13.3′, 13.3″, 13.4,13.4′, 13.4″, at least one transimpedance converter 13.10, 13.10′,13.10″, and at least first and second signal output conductors 13.8,13.8′, 13.8″, 13.9. Furthermore, the converter unit 1.3 comprises atleast one first electrical resistor 13.5, 13.5′, 13.5″, and/or at leastone second electrical resistor 13.6, 13.6′, 13.6″.

In a first embodiment of the acceleration transducer 1 as shown in FIGS.1 and 3 , the converter unit 1.3 is only and directly arranged on themain body 12. Preferably, the converter unit 1.3 is only and directlyarranged on a first normal side face 12.7 of the main body 12. In asecond embodiment of the acceleration transducer 1 as shown in FIGS. 2and 4 , the converter unit 1.3 is only arranged on a support 13.7. Thesupport 13.7 is made of electrically insulating material such as Al₂O₃,ceramics, Al₂O₃ ceramics, fiber-reinforced plastics, etc. The support13.7 is secured to the main body 12. Preferably, the support 13.7 isattached to the first normal side face 12.7 of the main body 12 by meansof material bonding such as gluing, soldering, etc.

The first and second piezoelectric element conductors 13.1, 13.1′,13.1″, 13.2, 13.2′, 13.2″, the first and second main body conductors13.3, 13.3′, 13.3″, 13.4, 13.4′, 13.4″, the first electrical resistor13.5, 13.5′, 13.5″, the second electrical resistor 13.6, 13.6′, 13. 6″,and the transimpedance converter 13.10, 13.10′, 13.10″ are attached to afirst normal side face 12.7 (first embodiment of the accelerationtransducer 1 according to FIGS. 1 and 3 ) or to the support 13.7 (secondembodiment of the acceleration transducer 1 according to FIGS. 2 and 4).

The first and second piezoelectric element conductors 13.1, 13.1′,13.1″, 13.2, 13.2′, 13.2″, the first and second main body conductors13.3, 13.3′, 13.3″, 13.4, 13.4′, 13.4″, and the first and second signaloutput conductors 13.8, 13.8′, 13.8″, 13.9 are made of electricallyconductive material such as copper, copper alloys, gold, gold alloys,aluminum, aluminum alloys, etc. and have a diameter of 0.02 mm to 0.10mm and are mechanically flexible.

The first and second piezoelectric element conductors 13.1, 13.1′,13.1″, 13.2, 13.2′, 13.2″, the first and second main body conductors13.3, 13.3′, 13.3″, 13.4, 13.4′, 13.4″ as well as first and secondsignal output conductors 13.8, 13.8′, 13.8″, 13.9 conduct first andsecond acceleration signals S1, S2 in a manner insulated from ground. Inthe context of the present invention, the term “insulated from ground”means electrically insulated from a grounding of the accelerationtransducer 1. Preferably, the housing 1.2 of the acceleration transducer1 is grounded; the housing 1.2 has the same electrical potential as thelocal ground. Thus, acceleration signals S1, S2 are conducted in amanner electrically insulated from an electrical potential of theacceleration transducer 1. In this way, the acceleration measurement isnot falsified by variations in the electrical potential of theacceleration transducer 1, for example between the housing 1.2 and theconverter unit 1.3.

Preferably, the first and second main body conductors 13.3, 13.3′,13.3″, 13.4, 13.4′, 13.4″ are patterned in an electrically conductivecoating. The electrically conductive coating is formed by chemical vapordeposition, physical vapor deposition, etc. The electrically conductivecoating is made of electrically conductive material such as copper,copper alloys, gold, gold alloys, platinum, platinum alloys, etc. Theelectrically conductive coating is an electrically conductive thin film.In the context of the present invention, the term “thin film” means thatthe thickness of the electrically conductive coating in a directionperpendicular to its planar extension is preferably less than 0.1 mm.The electrically conductive coating is applied directly to the firstnormal side face 12.7 (first embodiment of the acceleration transducer 1according to FIGS. 1 and 3 ) or the support 13.7 (second embodiment ofthe acceleration transducer 1 according to FIGS. 2 and 4 ). In thecontext of the present invention, the adverb “directly” means“immediately”. Preferably, patterning of the first and second main bodyconductors 13.3, 13.3′, 13.3″, 13.4, 13.4′, 13.4″ in the electricallyconductive coating is carried out by stenciling, photolithography andlaser ablation.

Preferably, the converter unit 1.3 comprises three first piezoelectricelement conductors 13.1, 13.1′, 13.1′ and three second piezoelectricelement conductors 13.2, 13.2′, 13.2″. One of the three firstpiezoelectric element electrical conductors 13.1, 13.1′, 13.1″ transmitsfirst acceleration signals S1 from the first electrically conductivecoating 101 of a respective one of the first, second or thirdpiezoelectric element 10, 10′, 10″ to the converter unit 1.3. Similarly,one of the three second piezoelectric element electrical conductors13.2, 13.2′, 13.2″ transmits second acceleration signals S2 from thesecond electrically conductive coating 102 of a respective one of thefirst, second or third piezoelectric element 10, 10′, 10″ to theconverter unit 1.3.

The first and second piezoelectric element conductors 13.1, 13.1′,13.1″, 13.2, 13.2′, 13.2″ are in contact with the first lateral surface130. This is because the first lateral surface 130 is available andplays a specific technical role, i.e. it has piezoelectric elementcontacts 13.01, 13.01′, 13.01″ provided thereon for transmitting thepiezoelectric charges which saves space. A first piezoelectric elementconductor 13.1, 13.1′, 13.1″ each contacts the first lateral surfaceelectrical coating 131 via a first piezoelectric element contact 13.01,13.01′, 13.01″. A second piezoelectric element conductor 13.2, 13.2′,13.2″ each contacts the second lateral surface electrical coating 133via a second piezoelectric element contact 13.02, 13.02′, 13.02″. Thefirst and second piezoelectric element contacts 13.01, 13.01′, 13.01″,13.02, 13.02′, 13.02″ are attached to the first lateral surface 130. Thefirst and second piezoelectric element contacts 13.01, 13.01′, 13.01″,13.02, 13.02′, 13.02″ are a material bond made by wire bonding,soldering, etc. Methods such as thermocompression bonding, thermosonicball wedge bonding, ultrasonic wedge bonding, etc. are suitable for wirebonding. The circular first and second piezoelectric element contacts13.01, 13.01′, 13.01″, 13.02, 13.02′, 13.02″ in FIG. 11 schematicallyrepresent formed wire.

The converter unit 1.3 preferably comprises three first and second mainbody conductors 13.3, 13.3′, 13.3″, 13.4, 13.4′, 13.4″. One firstpiezoelectric element conductor 13.1, 13.1′, 13.1″ each contacts a firstmain body conductor 13.3, 13.3′, 13.3″ via a first main body accesscontact 13.03, 13.03′, 13.03″. One second piezoelectric elementconductor 13.2, 13.2′, 13.2″ each contacts a second main body conductor13.4, 13.4′, 13.4″ via a second main body access contact 13.04, 13.04′,13.04″. The first and second main body access contacts 13.03, 13.03′,13.03″, 13.04, 13.04′, 13.04″ are attached to the first normal side face12.7 (first embodiment of the acceleration transducer 1 according toFIGS. 1 and 3 ) or to the support 13.7 (second embodiment of theacceleration transducer 1 according to FIGS. 2 and 4 ). The first andsecond main body access contacts 13.03, 13.03′, 13.03″, 13.04, 13.04′,13.04″ are a material bond made by wire bonding, soldering, etc. Methodssuch as thermocompression bonding, thermosonic ball wedge bonding,ultrasonic wedge bonding, etc. are suitable for wire bonding. Thecircular first and second main body access contacts 13.03, 13.03′,13.03″, 13.04, 13.04′, 13.04″ in FIG. 11 schematically represent formedwire.

The first electrical resistor 13.5, 13.5′, 13.5″, the second electricalresistor 13.6, 13.6′, 13.6″ and the transimpedance converter 13.10,13.10′, 13.10″ are electrically connected to each other by the firstmain body conductors 13.3, 13.3′, 13.3″. The second main body conductors13.4, 13.4′, 13.4″ with the second acceleration signals S2 of the first,second and third piezoelectric elements 10, 10′, 10″ are electricallyshort-circuited and at an electrical reference potential of theconverter unit 1.3. The electrical reference potential is a stabilized,i.e., temporally constant, direct electrical voltage.

Preferably, the converter unit 1.3 comprises three transimpedanceconverters 13.10, 13.10′, 13.10″. The three transimpedance converters13.10, 13.10′, 13.10″ have an identical structure. In the embodimentsaccording to FIGS. 1 and 2 , the transimpedance converter 13.10, 13.10′,13.10″ is an electronic component. The transimpedance converter 13.10,13.10′, 13.10″ is secured to the first normal side face 12.7 (firstembodiment of the acceleration transducer 1 according to FIGS. 1 and 3 )or to the support 13. 7 (second embodiment of the accelerationtransducer 1 according to FIGS. 2 and 4 ) by a material bond via anintermediate, and/or the transimpedance converter 13.10, 13.10′, 13.10″is secured to the first and second main body conductors 13.3, 13.3′,13.3″, 13.4, 13.4′, 13.4″ via the intermediate. The intermediate is anadhesive that can be chemically cured, an adhesive that can bephysically hardened, a solder, etc. Preferably, the intermediate is anadhesive such as epoxy, polyurethane, cyanoacrylate, methylmethacrylate, etc. One first main body conductor 13.3, 13.3′, 13.3″ eachcontacts a respective transimpedance converter 13.10, 13.10′, 13.10″.Any contacting method may be chosen. One first main body conductor 13.3,13.3′, 13.3″ each transmits first acceleration signals S1 to an input ofa transimpedance converter 13.10, 13.10′, 13.10″. Preferably, the inputof the transimpedance converter 13.10, 13.10′, 13.10′ has a highimpedance of more than 10⁷Ω. The transimpedance converter 13.10, 13.10′,13.10″ converts the first acceleration signals S1 into electricalvoltages. The converted first acceleration signals S1 are provided at anoutput of a transimpedance converter 13.10, 13.10′, 13.10″. Preferably,the output of the transimpedance converter 13.10, 13.10′, 13.10′ has alow impedance of less than 10²Ω. However, instead of using atransimpedance converter, those skilled in the art knowing the presentinvention may also use a charge amplifier with low electrical resistanceat an input of the charge amplifier.

FIG. 12 shows a schematic representation of a high-pass filter 18, 18′,18″ of the converter unit 1.3. Preferably, the converter unit 1.3comprises three first electrical resistors 13.5, 13.5′, 13.5″. The threefirst electrical resistors 13.5, 13.5′, 13.5″ are identical instructure.

In the embodiment according to FIGS. 1 and 2 , the first electricalresistor 13.5, 13.5′, 13.5″ is a resistive coating made of a resistivematerial such as Al₂O₃, ceramics, Al₂O₃ ceramics, etc. The resistivecoating is fabricated by chemical vapor deposition, physical vapordeposition, etc. The resistive coating is an electrical resistor thinfilm. Also, the resistive coating is a “thin film” in the sense of thepresent invention since its thickness in a direction perpendicular toits planar extension is preferably less than 0.1 mm. The resistivecoating is applied directly to the first normal side face 12.7 (firstembodiment of the acceleration transducer 1 according to FIGS. 1 and 3 )or the support 13.7 (second embodiment of the acceleration transducer 1according to FIGS. 2 and 4 ) and/or the resistive coating is applieddirectly to the first and second main body conductors 13.3, 13.3′,13.3″, 13.4, 13.4′, 13.4″. The resistive coating may be patterned bystenciling, photolithography, laser ablation, etc.

In the embodiment according to FIGS. 2 and 4 , the first electricalresistor 13.5, 13.5′, 13.5″ is an electrical component made of resistivematerial like ceramics, metal oxide, etc. and connecting wires.

A first main body conductor 13.3, 13.3′, 13.3″ each contacts a firstelectrical resistor 13.5, 13.5′, 13.5″. Any method of contacting may bechosen. A first electrical resistor 13.5, 13.5′, 13.5″ each iselectrically connected in parallel with one of the three piezoelectricelements 10, 10′, 10″. This connection in parallel is a high-pass filter18, 18′, 18″ because the first, second or third piezoelectric element10, 10′, 10″ is an electrical capacitor. The high-pass filter 18, 18′,18″ filters, i.e., eliminates, frequencies below a cut-off frequency.The cut-off frequency is preferably 10 Hz. When the accelerationmeasurement by the acceleration transducer 1 starts, a discharge of thefirst, second or third piezoelectric element 10, 10′, 10″ may lead tolow interference frequencies below the cut-off frequency. The lowinterference frequencies are present at the input of the transimpedanceconverter 13.10, 13.10′, 13.10″ and represent an undefined timeconstant. The low interference frequencies may falsify the accelerationmeasurement. Because the low interference frequencies are filtered, thetransimpedance converter 13.10, 13.10′, 13.10″ obtains a defined timeconstant. The cut-off frequency may be adjusted depending on the valueof the electrical resistance of the first electrical resistor 13.5,13.5′, 13.5″.

FIG. 13 shows a schematic representation of a low-pass filter 17, 17′,17″ of the converter unit 1.3. Preferably, the converter unit 1.3comprises three second electrical resistors 13.6, 13.6′, 13.6″. Thethree second electrical resistors 13.6, 13.6′, 13.6″ have an identicalstructure. The second electrical resistor 13.6, 13.6′, 13.6″ is anelectrical component made of resistive material such as ceramics, metaloxide, etc. and connecting wires. A first main body conductor 13.3,13.3′, 13.3″ each contacts a second electrical resistor 13.6, 13.6′,13.6″. Any method of contacting may be chosen. A second electricalresistor 13.6, 13.6′, 13.6″ each is electrically connected in serieswith one of the three piezoelectric elements 10, 10′, 10″. Thisconnection in series is a low-pass filter 17, 17′, 17″ because thefirst, second or third piezoelectric element 10, 10′, 10″ is anelectrical capacitor. The low-pass filter 17, 17′, 17″ filters, i.e.,eliminates, high interference frequencies above a natural frequency ofthe acceleration transducer 1. Such high interference frequencies aregenerated by mechanical excitation of the acceleration transducer 1. Thehigh interference frequencies are present at the input of thetransimpedance converter 13.10, 13.10′, 13.10″ and may saturate thetransimpedance converter 13.10, 13.10′, 13.10″ and thus falsify theacceleration measurement. The low-pass filter 17, 17′, 17″ may beadjusted to the natural frequency of the acceleration transducer 1depending on the value of the electrical resistance of the secondelectrical resistor 13.6, 13.6′, 13.6″.

Preferably, the converter unit 1.3 comprises three first main bodyoutput conductors 13.8, 13.8′, 13.8″. Each output of a transimpedanceconverter 13.10, 13.10′, 13.10″ contacts a first main body outputcontact 13.08, 13.08′, 13.08″ via a first main body conductor 13.3,13.3′, 13.3″. Preferably, the converter unit 1.3 comprises a second mainbody output conductor 13.9. The second main body conductors 13.4, 13.4′,13.4″ contact the second main body output conductor 13.9 via a secondmain body output contact 13.09. The first and second main body outputcontacts 13.08, 13.08′, 13.08″, 13.09 are secured to the first normalside face 12.7 (first embodiment of the acceleration transducer 1according to FIGS. 1 and 3 ) or to the support 13.7 (second embodimentof the acceleration transducer 1 according to FIGS. 2 and 4 ). The firstand second main body output contacts 13.08, 13.08′, 13.08″, 13.09 are amaterial bond made by wire bonding, soldering, etc. Methods such asthermocompression bonding, thermosonic ball wedge bonding, ultrasonicwedge bonding, etc. are suitable for wire bonding. The circular firstand second main body exit contacts 13.08, 13.08′, 13.08″, 13.09 in FIG.11 schematically represent formed wire.

The first main body output conductors 13.8, 13.8′, 13.8″ transmitconverted first acceleration signals S1 to the signal output 1.4. Thesecond main body output conductor 13.9 transmits the sum of the secondacceleration signals S2 to the signal output 1.4.

The signal output 1.4 is secured to the housing 1.2 in some regions ofthe housing 1.2. According to the embodiments of the accelerationtransducer 1 as shown in FIGS. 1 and 2 , the signal output 1.4preferably is an electric cable. As schematically shown in FIG. 14 , thesignal output 1.4 comprises signal conductors 14.1, 14.1′, 14.1″, 14.2,a protective sheath 14.3, a sheath flange 14.4, an electrical insulation14.5 and casting compound 14.6.

In cross-section, the signal output 1.4 has a multilayer structure.

The signal conductors 14.1, 14.1′, 14.1″, 14.2 form an inner layer.Preferably, the signal output 1.4 comprises three first signalconductors 14.1, 14.1′, 14.1″ and one second signal conductor 14.2. Thesignal conductors 14.1, 14.1′, 14.1″, 14.2 are made of electricallyconductive material such as copper, copper alloys, gold, gold alloys,aluminum, aluminum alloys, etc. Preferably, each signal conductor 14.1,14.1′, 14.1″, 14.2 comprises an electrically insulating sheath. Thefirst and second main body output conductors 13.8, 13.8′, 13.8″, 13.9contact first and second signal conductors 14.1, 14.1′, 14.1″, 14.2. Afirst main body output conductor 13.8, 13.8′, 13.8″ each contacts arespective first signal conductor 14.1, 14.1′, 14.1″. The second mainbody output conductor 13.9 contacts the second signal conductor 14.2.

As schematically shown in FIG. 14 , the electrical insulation 14.5 formsa middle layer and is arranged around the signal conductors 14.1, 14.1′,14.1″, 14.2. The electrical insulation 14.5 electrically insulates thesignal conductors 14.1, 14.1′, 14.1″, 14.2 from the protective sheath14.3. The electrical insulation 14.5 is made of electrically insulatingmaterial such as Al₂O₃, ceramics, Al₂O₃ ceramics, fiber-reinforcedplastics, etc.

The protective sheath 14.3 forms an outer layer. The protective sheath14.3 protects the electrical insulation 14.5 as well as the signalconductors 14.1, 14.1′, 14.1″, 14.2 from harmful environmental impactssuch as contamination (dust, moisture, etc.) as well as fromelectromagnetic waves which may lead to undesirable interference effectsin the first and second acceleration signals S1, S2. The protectivesheath 14.3 is made of mechanically resistant material such as metal,plastics, etc.

FIGS. 14 to 18 show steps in the assembly of the embodiment of theacceleration transducer 1 according to FIG. 2 .

FIG. 14 shows a first step in the assembly in which signal conductors14.1, 14.1′, 14.1″, 14.2 are introduced into the housing 1.2. Thehousing 1.2 comprises a signal output opening 1.22. Preferably, thesignal output opening 1.22 has the shape and dimensions of the outerdiameter of the protective sheath 14.3. The ends of the signalconductors 14.1, 14.1′, 14.1″, 14.2 are stripped while the electricallyinsulating sheath is removed in some regions here. The ends of thesignal conductors 14.1, 14.1′, 14.1″, 14.2 project through the signaloutput opening 1.22 into an inner space of the housing 1.2. The innerspace of the housing 1.2 is the space around the housing bottom 1.23.

The signal output opening 1.22 is sealed from the outside by theprotective sheath 14.3 and the sheath flange 14.3. Preferably, one endof the protective sheath 14.3 is attached to the sheath flange 14.4. Thesheath flange 14.4 is made of mechanically resistant material such asmetal, plastics, etc. The connection of protective sheath 14.3 andsheath flange 14.4 is achieved by a force connection such as crimping,etc.

The metal flange 14.4 itself is fastened to the housing 1.2 by amaterial bond. Preferably, the metal flange 14.4 is fastened to an outeredge of the housing opening 1.22 that faces away from the interior ofthe housing 1.2. The material bond is made by welding, soldering,gluing, etc. The connection between the sheath flange 14.4 and thehousing 1.2 causes a relief of strain on the protective sheath 14.3. Dueto this strain relief of the protective sheath 14.3, mechanical loadsare not transmitted from the protective sheath 14.3 into the interior ofthe housing 1.2 where they may reach the converter unit 1.3 and causedamage such as tearing or rupture of main body output conductors 13.8,13.8′, 13.8″, 13.9. Such mechanical stresses originate from twisting,torsion, etc. of the protective sheath 14.3 about its extension alongthe longitudinal axis.

FIG. 15 shows a second step in the assembly in which the signalconductors 14.1, 14.1′, 14.1″, 14.2 are cast with casting compound 14.6within the housing 1.2. The casting compound 14.6 is applied through thehousing opening 1.20 to the signal conductors 14.1, 14.1′, 14.1″, 14.2in the signal output opening 1.21. The casting compound 14.6 is anadhesive that can be chemically cured or an adhesive that can bephysically hardened or a combination of a chemically cured adhesive anda physically hardened adhesive. Preferably, the casting compound 14.6consists of an adhesive such as epoxy, polyurethane, cyanoacrylate,methyl methacrylate, etc. The casting compound 14.6 is an electricalinsulator having an electrical resistivity of more than 10¹²≠mm²/m.Preferably, enough casting compound 14.6 to completely seal the signaloutput opening 1.21 is applied to the signal conductors 14.1, 14.1′,14.1″, 14.2 in the signal output opening 1.21.

FIG. 16 shows a third step in the assembly in which the signalconductors 14.1, 14.1′, 14.1″, 14.2 cast in casting compound 14.6 areexposed in some areas within the housing 1.2. The exposure 14.7 of thesignal conductors 14.1, 14.1′, 14.1″, 14.2 is achieved by a suitablecutting tool such as a cutting wedge, a milling cutter, etc. The cuttingtool is introduced into the interior of the housing 1.2 through thehousing opening 1.20 and cuts off the ends of the signal conductors14.1, 14.1′, 14.1″, 14.2 as well as a portion of the cured castingcompound 14.6. The exposure 14.7 is in a horizontal plane defined by thetransverse axis x and the longitudinal axis y. In the area of theexposure 14.7, the end faces of cut ends of the signal conductors 14.1,14.1′, 14.1″, 14.2 are exposed in one plane. Preferably, the plane isparallel to the housing opening 1.20. In the area of the exposure 14.7,the lateral surfaces of the signal conductors 14.1, 14.1′, 14.1″, 14.2are completely covered by casting compound 14.6. The casting compound14.6 secures the signal conductors 14.1, 14.1′, 14.1″, 14.2 in astrain-relieved manner. Due to this strain relief of the signalconductors 14.1, 14.1′, 14.1″, 14.2, mechanical loads are nottransmitted from the signal conductors 14.1, 14.1′, 14.1″, 14.2 into theinterior of the housing 1.2 where they may reach the converter unit 1.3and lead to damage such as a tearing or rupture of main body outputconductors 13.8, 13.8′, 13.8″, 13.9. Such mechanical stresses originatefrom twisting, torsion, etc. of signal conductors 14.1, 14.1′, 14.1″,14.2 about their extension along the longitudinal axis. Furthermore, thecasting compound 14.6 seals the signal output opening 1.21 in agas-tight manner. The gas-tight seal of the signal output opening 1.21prevents moisture from entering via the signal conductors 14.1, 14.1′,14.1″, 14.2 into the interior of the housing 1.2 up to the transducerunit 1.1 where moisture might impair the functioning of thepiezoelectric elements 10, 10′, 10″ since piezoelectric material such asquartz is strongly hygroscopic.

FIG. 17 shows a fourth step in the assembly in which the transducer unit1.1 is introduced into the housing 1.2. The transducer unit 1.1 togetherwith the converter unit 1.3 is introduced through the housing opening1.20 into the interior of the housing 1.2. The second normal side face12.6 is secured to the housing bottom 1.23 by means of a material bondsuch as bonding, soldering, etc. Preferably, the transducer unit 1.1 isarranged with the fourth tangential side face 12.4 in the proximity ofthe exposure 14.7.

FIG. 18 shows a fifth step in the assembly in which the converter unit1.3 of the transducer unit 1.1 is contacted. Contacting of the converterunit 1.3 is performed by a suitable contacting tool such as a wirebonder, etc. The contacting tool is introduced into the interior of thehousing 1.2 through the housing opening 1.20. The contacting toolconnects first and second main body conductors 13.3, 13.3′, 13.3″, 13.4,13.4′, 13.4″ of the converter unit 1.3 via first and secondpiezoelectric element conductors 13.1, 13.1′, 13.1″, 13.2, 13.2′, 13.2″to the first lateral surface 130 of the first, second or thirdpiezoelectric element 10, 10′, 10″. In addition, the contacting toolconnects first and second main body conductors 13.3, 13.3′, 13.3″, 13.4,13.4′, 13.4″ of the converter unit 1.3 to the signal conductors 14.1,14.1′, 14.1″, 14.2 of the signal output 1.4 via first and second mainbody output conductors 13.8, 13.8′, 13.8″, 13.9.

Preferably, the first and second main body output conductors 13.8,13.8′, 13.8″, 13.9 are directly connected to end faces of cut ends ofthe signal conductors 14.1, 14.1′, 14.1″, 14.2. This direct contactingof the first and second main body output conductors 13.8, 13.8′, 13.8″,13.9 with the signal conductors 14.1, 14.1′, 14.1″, 14.2 has theadvantage that no further supporting means such as a printed circuitboard, etc. is necessary which keeps the dimensions and weight of theacceleration transducer low and makes the assembly of the accelerationtransducer simple and inexpensive. This direct contacting of the firstand second main body output conductors 13.8, 13.8′, 13.8″, 13.9 with thesignal conductors 14.1, 14.1′, 14.1″, 14.2 has the further advantagethat the converter unit 1.3 is connected to the signal conductors 14.1,14.1′, 14.1″, 14.2 in a strain-relieved manner by the mechanicallyflexible main body output conductors 13.8, 13.8′, 13. 8″, 13.9, i.e.,the mechanically flexible main body output conductors 13.8, 13.8′,13.8″, 13.9 damp mechanical stresses penetrating up to the signalconductors 14.1, 14.1′, 14.1″, 14.2.

When the electrical contacting of the converter unit 1.3 is completed,the housing opening 1.20 is sealed in a gas-tight manner by the housingcover 1.21. The seal is made by material bonding such as welding,soldering, gluing, etc.

LIST OF REFERENCE NUMERALS

-   1 acceleration transducer-   1.1 transducer unit-   1.2 housing-   1.20 housing opening-   1.21 housing cover-   1.22 signal output opening-   1.23 housing bottom-   1.24 assembly gap-   1.3 converter unit-   1.4 signal output-   10, 10′, 10″ piezoelectric element-   11, 11′, 11″ seismic mass-   12 main body-   12.1, 12.2, 12.3, 12.4 tangential side face-   12.6, 12.7 normal side face-   13.01, 13.01′, 13.01″ first piezoelectric element contact-   13.02, 13.02′, 13.02″ second piezoelectric element contact-   13.03, 13.03′, 13.03″ first main body access contact-   13.04, 13.04′, 13.04″ second main body access contact-   13.08, 13.08′, 13.08″ first main body output contact-   13.09 second main body output contact-   13.1, 13.1′, 13.1″ first piezoelectric element conductor-   13.2, 13.2′, 13.2″ second piezoelectric element conductor-   13.3, 13.3′, 13.3″ first main body conductor-   13.4, 13.4′, 13.4″ second main body conductor-   13.5, 13.5′, 13.5″ first electrical resistor-   13.6, 13.6′, 13.6″ second electrical resistor-   13.7 support-   13.8, 13.8′, 13.8″ first main body output conductor-   13.9 second main body output conductor-   13.10, 13.10′, 13.10″ transimpedance converter-   14.1, 14.1′, 14.1″ first signal conductor-   14.2 second signal conductor-   14.3 protective sheath-   14.4 sheath flange-   14.5 electrical insulation-   14.6 casting compound-   14.7 exposure-   15, 15′, 15″ inner connecting means-   16, 16′, 16″ outer connecting means-   17, 17′, 17″ low pass filter-   18, 18′, 18″ high pass filter-   101 first electrically conductive coating-   102 second electrically conductive coating-   110, 120 end face-   111, 111′ first electrically conductive end face coating-   112, 112′, 112″ first uncoated end face area-   121-121′″ second electrically conductive end face coating-   122, 122′, 122″ second uncoated end face area-   130, 140, 150, 160 lateral surface-   131, 131′ first electrically conductive lateral surface coating-   132, 132′-132″″ first uncoated lateral surface area-   133, 133′ further first electrically conductive lateral surface    coating-   141 second electrically conductive lateral surface coating-   142, 142′, 142″ second uncoated lateral surface area-   151, 151′ third electrically conductive lateral surface coating-   161 fourth electrically conductive lateral surface coating-   a normal axis-   F force-   h principal tangential axis-   n secondary tangential axis-   S1, S2 acceleration signals-   x transverse axis-   y longitudinal axis-   z vertical axis

What is claimed is:
 1. An acceleration transducer arranged in arectangular coordinate system with three mutually orthogonal axes, oneof the three axes being a transverse axis, one of the three axes being alongitudinal axis, and one of the three axes being a vertical axis, theacceleration transducer comprising: a main body that defines a firsttangential side face lying in a first plane, a second tangential sideface lying in a second plane that is disposed spaced apart from andnormal to the first plane, a third tangential side face lying in a thirdplane that is disposed spaced apart from and parallel to the firstplane, and a fourth tangential side face lying in a fourth plane that isdisposed spaced apart from and parallel to the second plane, whereineach of the first, second, third and fourth tangential side faces isdisposed tangentially to the vertical axis; wherein the main bodyfurther defines a lower normal side face lying in a fifth plane that isnormal to each of the first, second, third and fourth planes, andwherein the main body further defines an upper normal side face lying ina sixth plane that is disposed spaced apart along the vertical axis fromand parallel to the fifth plane; exactly three piezoelectric elements,which include only a first piezoelectric element secured to the firsttangential side face, a second piezoelectric element secured to thesecond tangential side face, and a third piezoelectric element securedto the third tangential side face; wherein the first piezoelectricelement has a high sensitivity for a shear force acting along thelongitudinal axis being the principal tangential axis, a low sensitivityfor a shear force acting along the vertical axis being a secondarytangential axis and a low sensitivity for a normal force acting alongthe transverse axis being a normal axis: wherein the secondpiezoelectric element has a high sensitivity for a shear force actingalong the transverse axis being the principal tangential axis, a lowsensitivity for a shear force acting along the vertical axis being thesecondary tangential axis and a low sensitivity for a normal forceacting along the longitudinal axis being the normal axis; wherein thethird piezoelectric element has a high sensitivity for a shear forceacting along the vertical axis being the principal tangential axis, alow sensitivity for a shear force acting along the longitudinal axisbeing the secondary tangential axis and a low sensitivity for a normalforce acting along the transverse axis being the normal axis, whereineach of the three piezoelectric elements comprises at least one end facethat comprises at least one electrically conductive end face coating;wherein the electrically conductive end face coating is configured toreceive piezoelectric charges generated for the shear force acting alongthe principal tangential axis; wherein the electrically conductive endface coating is configured to receive piezoelectric interference chargesgenerated for the shear force acting along the secondary tangentialaxis; wherein each of the three piezoelectric elements comprises atleast one lateral surface that comprises at least one electricallyconductive lateral surface coating; wherein the electrically conductivelateral surface coating is configured to receive piezoelectricinterference charges generated for the normal force acting along thenormal axis: exactly three seismic masses, which include only a firstseismic mass secured to the first piezoelectric element so that a firstacceleration of the first seismic mass exerts on the first piezoelectricelement a first shear force proportional to the first acceleration, asecond seismic mass secured to the second piezoelectric element so thata second acceleration of the second seismic mass exerts on the secondpiezoelectric element a second shear force proportional to the secondacceleration, and a third seismic mass secured to the thirdpiezoelectric element so that a third acceleration of the third seismicmass exerts on the third piezoelectric element a third shear forceproportional to the third acceleration; and wherein each of the threepiezoelectric elements has a high sensitivity for a shear force exertedby the respective seismic mass attached thereto along a principaltangential axis that is other than one of the three mutually orthogonalaxes for each of the three piezoelectric elements.
 2. The accelerationtransducer according to claim 1, wherein each of the three piezoelectricelements comprises end faces, wherein each end face defines an end faceplane that is defined by the principal tangential axis and is secondarytangential axis; which secondary tangential axis is defined in a planeperpendicular to the principal tangential axis, and defining a normalaxis that is normal to the end face plane; wherein each of the threepiezoelectric elements defines lateral surfaces, wherein each lateralsurface is disposed parallel to the normal axis; wherein each of thethree piezoelectric elements is configured to generate piezoelectriccharges on the end faces under the action of a shear force along theprincipal tangential axis; wherein each of the three piezoelectricelements has a low sensitivity for a shear force exerted by the seismicmass attached thereto along the secondary tangential axis, wherein eachof the three piezoelectric elements is configured to generatepiezoelectric interference charges on the end faces under the action ofa shear force along the secondary tangential axis; wherein each of thethree piezoelectric elements has a low sensitivity for a normal forceexerted by the seismic mass attached thereto along the normal axis; andwherein each of the three piezoelectric elements is configured togenerate piezoelectric interference charges on said lateral surfacesunder the action of a normal force acting along the normal axis.
 3. Theacceleration transducer according to claim 1, wherein each of the threepiezoelectric elements with a high sensitivity for a shear force alongthe principal tangential axis is configured to generate at least by afactor of 5 more piezoelectric charges per unit force than with a lowsensitivity for a shear force acting along the secondary tangential axisor with a low sensitivity for a normal force acting along the normalaxis.
 4. The acceleration transducer according to claim 1, wherein foreach of the three piezoelectric elements, the electrically conductiveend face coating and the electrically conductive lateral surface coatingform a continuous electrically conductive coating; and wherein each ofthe three piezoelectric elements is configured so that the piezoelectricinterference charges generated for the shear force acting along thesecondary tangential axis have a polarity opposite to the polarity ofthe piezoelectric interference charges generated for the normal forceacting along the normal axis.
 5. The acceleration transducer accordingto claim 4, wherein the electrically conductive lateral surface coatingof each of the three piezoelectric elements defines a size that isconfigured so that the continuous electrically conductive coatingreceives essentially the same number of piezoelectric interferencecharges for the shear force acting along the secondary tangential axisand for the normal force acting along the normal axis so that theopposite polarities of the same number of piezoelectric interferencecharges neutralize each other.
 6. The acceleration transducer accordingto claim 4, wherein for each of the three piezoelectric elements, thelateral surface comprises a first lateral surface that is normal to thetangential axis of the piezoelectric element; wherein the first lateralsurface comprises a first electrically conductive lateral surfacecoating and a further first electrically conductive lateral surfacecoating; wherein the first electrically conductive lateral surfacecoating defines a first size; wherein the further first electricallyconductive lateral surface coating defines a second size; wherein theratio of the first size of the first electrically conductive lateralsurface coating to the second size of the further first electricallyconductive lateral surface coating is configured so that the continuouselectrically conductive coating receives essentially the same number ofpiezoelectric interference charges for the shear force acting along thesecondary tangential axis and for the normal force acting along thenormal axis so that the opposite polarities of the same number ofpiezoelectric interference charges neutralize each other.
 7. Theacceleration transducer according to claim 6, further comprising: firstand second piezoelectric element conductors; wherein for each of thethree piezoelectric elements, the first electrically conductive lateralsurface coating is materially bonded to the first piezoelectric elementconductor; wherein for each of the three piezoelectric elements, thefurther first electrically conductive lateral surface coating ismaterially bonded to the second piezoelectric element conductor; whereinthe first piezoelectric element conductor is configured to transmitpiezoelectric charges as first acceleration signals from a firstcontinuous electrically conductive coating; and wherein the secondpiezoelectric element conductor is configured to transmit piezoelectriccharges as second acceleration signals from a second continuouselectrically conductive coating.
 8. The acceleration transduceraccording to claim 1, wherein for each of the three piezoelectricelements, the electrically conductive end face coating fits closely tothe end face by material bonding and seals microscopic pores in the endface; wherein the electrically conductive lateral surface coating isapplied to the lateral surface by material bonding and sealingmicroscopic pores in the lateral surface; and wherein as a result of thesealing of the microscopic pores the piezoelectric element requires nomechanical pre-loading.
 9. The acceleration transducer according toclaim 1, wherein for each of the three piezoelectric elements, the endface comprises a first end face and a second end face, wherein each ofthe first and second end faces is arranged in a manner opposite to thenormal axis of the piezoelectric element; wherein the first end facecomprises a first electrically conductive end face coating; wherein thesecond end face comprises a second electrically conductive end facecoating; wherein the lateral surface comprises a first lateral surfacethat is disposed normal to the secondary tangential axis of thepiezoelectric element; wherein the first lateral surface comprises afirst electrically conductive lateral surface coating and a furtherfirst electrically conductive lateral surface coating; wherein the firstelectrically conductive end face coating and the first electricallyconductive lateral surface coating form a first continuous electricallyconductive coating; and wherein the second electrically conductive endface coating and the further first electrically conductive lateralsurface coating form a second continuous electrically conductivecoating.
 10. The acceleration transducer according to claim 8, whereinfor each of the three piezoelectric elements, the lateral surfacecomprises at least one second lateral surface and at least one thirdlateral surface, wherein each of said second and third lateral surfacesis disposed normal to the principal tangential axis of the piezoelectricelement; wherein the second lateral surface comprises a secondelectrically conductive lateral surface coating; wherein the thirdlateral surface comprises a third electrically conductive lateralsurface coating; and wherein each of the second and third electricallyconductive lateral surface coatings is part of a first continuouselectrically conductive coating or part of a second continuouselectrically conductive coating.
 11. The acceleration transduceraccording to claim 8, wherein for each of the three piezoelectricelements, the lateral surface thereof comprises at least one secondlateral surface and at least one third lateral surface, wherein each ofthe second and third lateral surfaces is disposed normal to theprincipal tangential axis of the piezoelectric element; wherein thesecond lateral surface comprises a second electrically conductivelateral surface coating; wherein the third lateral surface comprises athird electrically conductive lateral surface coating; and wherein thethird electrically conductive lateral surface coating is part of a firstcontinuous electrically conductive coating and the second electricallyconductive lateral surface coating is part of a second continuouselectrically conductive coating.
 12. The acceleration transduceraccording to claim 8, wherein for each of the three piezoelectricelements, the lateral surface comprises at least one second lateralsurface and at least one fourth lateral surface, wherein the secondlateral surface is disposed normal to the principal tangential axis ofthe piezoelectric element, wherein the fourth lateral surface isdisposed normal to the secondary tangential axis of the piezoelectricelement; wherein the second lateral surface comprises a secondelectrically conductive lateral surface coating; wherein the fourthlateral surface comprises a fourth electrically conductive lateralsurface coating; and wherein each of the second and fourth electricallyconductive lateral surface coatings is part of a first continuouselectrically conductive coating or part of a second continuouselectrically conductive coating.
 13. The acceleration transduceraccording to claim 8, wherein for each of the three piezoelectricelements, the lateral surface comprises at least one third lateralsurface and at least one fourth lateral surface, wherein third lateralsurface is disposed normal to the principal tangential axis of thepiezoelectric element, wherein the fourth lateral surface is disposednormal to the secondary tangential axis of the piezoelectric element;wherein the third lateral surface comprises a third electricallyconductive lateral surface coating; wherein the fourth lateral surfacecomprises a fourth electrically conductive lateral surface coating;wherein the third electrically conductive lateral surface coating ispart of a first continuous electrically conductive coating, and whereinthe fourth electrically conductive lateral surface coating is part of asecond continuous electrically conductive coating.